The present invention relates to an ink cartridge for supplying ink in a proper negative pressure state to a recording head that ejects ink droplets in response to print signals.
This invention also involves a method for regulating the flow of fluid from an ink cartridge to an ink jet head.
An ink jet recording apparatus is generally configured such that an ink jet recording head for ejecting ink droplets in response to print signals is mounted on a carriage reciprocating in a sheet width direction across a piece of recording paper, and ink is supplied from an external ink tank to the recording head. In case of a small recording apparatus, an ink storage container such as an ink tank is arranged to be removable from the carriage in view of convenience in handling and to facilitate replacement of an exhausted ink tank with a fresh ink tank containing a new supply of ink (or inks, if the tank is a multi-color tank).
In order to prevent leakage of ink from the recording head, such an ink storage container generally includes therein a porous member impregnated with ink so that the capillary force of the porous member holds the ink.
In addition, there is a tendency for the amount of ink consumed to increase, with time, because the continuing development of improved printers leads to an increased number of nozzle openings in order to keep pace with required improvement in print quality and print speed.
In order to accommodate these developments in ink jet printer design, it is preferable to increase the amount of ink that can be stored in the ink storage container, but this leads to an increase in the volume of the porous member. However, in the case where the porous member that holds the ink employs capillary force, the height, i.e. water head, of the porous member is limited, and therefore the bottom area of the ink storage container must be increased in order to increase the container's volume, causing a problem in which the carriage size and thus entire size of the recording apparatus must be increased.
To solve this problem, Japanese Patent Kokai Publication No. Hei. 8-174860 proposes, at paragraphs 0041-0043, and FIG. 10, an ink cartridge in which a membrane member deformable by ink pressure is formed at its center with a through-hole to provide a membrane valve seat, and a valve member is provided at a location opposing the membrane valve seat.
Also to solve this problem, International Patent Publication No. PCT00/03877 proposes an ink cartridge in which a valve member is formed by injection molding of polymer material having elasticity, a through-hole is formed in a center of the valve member, a back surface of the valve member is pressingly contacted with a sealing member by a spring, and the valve member is moved by a negative pressure acting on the back surface of the valve member so that ink flows out via the through-hole to an ink supply port.
Meanwhile, an ink cartridge having high ink supply performance and which can supply a large amount of ink to a recording head, is needed in order to satisfy the need for such cartridges when used in high speed printing. The most important factor affecting the performance when supplying ink to a recording head is the flow passage resistance within the cartridge.
U.S. Pat. No. 4,602,662 describes an externally-controlled valve for use in liquid marking systems. This reference teaches that an inlet and outlet are located on one side of a movable member, and a spring and external vacuum source are located on the other side of the movable member. The patent specifically states that the spring is not used to seal the valve, but rather, is provided only to prevent siphoning, and the external vacuum source serves to keep the valve closed.
U.S. Pat. No. 4,971,527 involves a regulator valve for an ink marking system. A diaphragm is pressed between two springs and so serves to dampen pressure pulsations in the ink flowing between an inlet and outlet located on one side of the diaphragm.
U.S. Pat. No. 5,653,251 relates to a vacuum actuated sheath valve. While an inlet and outlet are located on the same side of the valve membrane, that membrane itself can perforated, allowing liquid to pass to the other side of the membrane. Moreover, the membrane is stretched over a curved projection, and no spring is used to regulating the valve “cracking” pressure. More specifically, U.S. Pat. No. 5,653,251 discloses a valve structure having a valve member made of an elastically deformable membrane, a convex portion with which the valve member is contactable, and a flow channel formed in the convex portion and closable by the valve member. In the valve structure, negative pressure at the demand side is applied to one surface of the valve member to separate the valve member from the flow channel, to thereby control supply and interruption of the liquid. However, in the valve open state, the area of the valve member receiving the liquid pressure (the pressure-receiving area) is extremely small, meaning that the difference in area between the front and back surfaces of the valve member is large. For this reason, the valve open state cannot be maintained by the small pressure change which results from ink consumption by the recording head. When the valve structure is put into the valve closed state, the pressure-receiving area is extremely large, so that the valve structure is returned to the valve open state. Accordingly, there is a problem in that this operation is undesirably repeated to cause pulsations during the supply of ink, which, it will be appreciated, can adversely affect printing.
In the ink cartridge disclosed in International Patent Publication No. PCT00/03877, the through-hole, which forms an ink flow passage through the membrane member, causes a fluidic resistance, and further, a mutual clearance of the through-hole with respect to the valve member cooperating with the through-hole also causes a large fluidic resistance.
European Patent Application No. 1 199 178 describes an ink cartridge having a differential pressure valve mechanism (U.S. Patent Application Publn. No. 2002/0109760 is a counterpart). This reference describes valves in which a perforation in a movable membrane is urged by a spring to abut a solid projection.
To reduce the fluidic resistance caused by the through-hole of the membrane member, it is conceivable to make the diameter of the through-hole larger, but since the membrane member must be formed from elastic polymer material, increasing the size of the through-hole will reduce the load per unit area, causing a decrease in the sealing pressure, and thus degrading the valve's sealing ability and reducing cartridge performance.
For this reason, a modification can be made wherein a protruding portion is formed in the region of the valve member opposing the sealing member to improve the sealing ability, and the through-hole is formed through this protruding portion. However, due to the biasing force of the spring, when the valve is maintained in the closed state, the protruding portion is elastically deformed and collapsed.
Consequently, even when negative pressure acts on the valve member to move the valve backward from the sealing member by an amount corresponding to the applied negative pressure, the protruding portion that has been elastically deformed is returned to the original state, and so a flow passage resistance at the valve open state is high. In the case where a large amount of ink is needed for consumption, such as when printing an image, there is a possibility that insufficient ink will be supplied.
Further, in order to stabilize the closed state of the valve member, the protruding portion needs to be sufficiently collapsed to be in close contact with the sealing member. To this end, the protruding portion of the valve member is constructed from an elastic member made of elastomer. Also, the protruding portion of the valve member is thick in comparison to a membrane surface of the valve member receiving the differential pressure. Therefore, a turbulent flow of resin is likely to occur during injection molding, and thus welds are likely to occur as a consequence of molding, causing difficulty in formation of the protruding portion of the valve member largely protruded from the membrane surface.
Moreover, since an offset in concentricity between the protruding portion of the valve member and the sealing member is caused due to fluctuation in component precision and assembly, the contact surface of the sealing member must be made large in comparison with the diameter of the valve member protruding portion in order to insure proper alignment.
Because of these considerations, the sealing member is present over a wide area around the protruding portion of the valve member, causing the problem of large flow passage resistance.
Further, because the through-hole must be formed through the protruding portion of the valve member, wrinkles or grooves due to welds are likely to occur in a sealing region, causing poor manufacture yields, which are undesirable.
Moreover, in the case where a through-hole configuration, such as a tapered configuration, is applied to the through-hole formed in the membrane member as an attempt to decrease a flow passage resistance, a lower portion of the protruded portion is small in wall thickness, causing a problem in which the protruded portion is deformed into the interior of the through-hole. That is, there is a further problem in that the configuration of the through-hole is limited.